Molecular sieve materials, both natural and synthetic, have been demonstrated in the past to be useful as adsorbents and to have catalytic properties for various types of hydrocarbon conversion reactions. Certain molecular sieves, such as zeolites, AlPOs, and mesoporous materials, are ordered, porous crystalline materials having a definite crystalline structure as determined by X-ray diffraction (XRD). Within the crystalline molecular sieve material there are a large number of cavities which may be interconnected by a number of channels or pores. These cavities and pores are uniform in size within a specific molecular sieve material. Because the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as “molecular sieves” and are utilized in a variety of industrial processes.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as rigid three-dimensional framework of SiO4 and Periodic Table Group 13 element oxide (e.g., AlO4). The tetrahedra are cross-linked by the sharing of oxygen atoms with the electrovalence of the tetrahedra containing the Group 13 element (e.g., aluminum) being balanced by the inclusion in the crystal of a cation, for example a proton, an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group 13 element (e.g., aluminum) to the number of various cations, such as H+, Ca2+/2, Sr2+/2, Na+, K+, or Li+, is equal to unity.
Molecular sieves that find application in catalysis include any of the naturally occurring or synthetic crystalline molecular sieves. Examples of these molecular sieves include large pore zeolites, intermediate pore size zeolites, and small pore zeolites. These zeolites and their isotypes are described in “Atlas of Zeolite Framework Types”, eds. Ch. Baerlocher, L. B. McCusker, D. H. Olson, Elsevier, Sixth Revised Edition, 2007, which is hereby incorporated by reference. A large pore zeolite generally has a pore size of at least about 7 Angstroms, an intermediate pore size zeolite generally has a pore size from about 5 Angstroms to less than about 7 Angstroms and includes, and a small pore size zeolite has a pore size from about 3 Angstroms to less than about 5.0 Angstroms.
Intermediate pore size zeolites include those having the EUO framework type. Referring to the above-mentioned Atlas of Zeolite Framework Types, EUO framework type zeolites have a uni-dimensional microporous crystalline framework, with channels having diameters of 4.1×5.4 Angstroms, with large side pockets. According to N. A. Briscoe et al., Zeolites 8, 74-76 (1988), the lateral pockets have a depth of 8.1 Angstroms and a diameter of 6.8×5.8 Angstroms.
Molecular sieves with the EUO framework type include EU-1, TPZ-3 and ZSM-50. Zeolite EU-1 and zeolite TPZ-3, as well as their preparation from a synthesis mixture comprising a N,N,N,N′,N′,N′-hexamethyl-1,6-hexamethylene diammonium compound as structure directing agent are described in EP-A-0,042,226 and in EP-A-0,051,318. U.S. Pat. No. 4,640,829 discloses ZSM-50 zeolite and its synthesis in the presence of dibenzyldimethylammonium ions as a structure directing agent.
In an article entitled “Reinvestigation into the synthesis of zeolites using diquaternary alkylammonium ions (CH3)3N+(CH2)nN+(CH3)3, with n=3-10 as structure-directing agents”, in Microporous and Mesoporous Materials, 68, 97-104 (2004), Lee et al. report that Me6-diquat-5 cations [(CH3)3N+(CH2)5N+(CH3)3, also referred to as N,N,N,N′,N′,N′-hexamethylpentanediammonium] exhibit a wide diversity of phase selectivity by directing the synthesis of EU-1, ZSM-12, ZSM-48, MCM-22 or mordenite depending on the oxide composition of the synthesis mixture.
A later article entitled “N,N,N,N′,N′,N′-hexamethylpentanediammonium-MWW precursor: A reaction intermediate in the synthesis of zeolites TNU-9 and EU-1”, by Shin et al in Microporous and Mesoporous Materials, 124, 227-231 (2009) reports that the layered precursor of the zeolite MCM-22, generally referred to as MCM-22(P), is a reaction intermediate in the synthesis of zeolites TNU-9 and EU-1 in the presence of Me6-diquat-5 cations, depending on the Na+ content of the synthesis mixture.
U.S. Pat. No. 6,514,479 discloses EUO framework type zeolite crystals having a size of less than 5 μm, wherein at least a portion of the EUO zeolite crystals is in the form of crystal aggregates with a specific granulometry such that the value of Dv,90 is in the range of 200 μm to 40 μm. According to this document, this means that, when analyzed by laser diffraction granulometry after being subjected to ultrasound, 90% of the aggregates have an equivalent sphere diameter in the range of 200 μm to 40 μm. The crystals are synthesized using alkylated polymethylene α-ω diammonium salts, preferably 1,6-N,N,N,N′,N′,N′-hexamethylhexamethylenediammonium salts, as structure directing agent and in the presence of seeds of one or more zeolites of the framework type EUO, LTA, LTL, FAU, MOR, MAZ, OFF, FER, ERI, BEA, MFI, MTW, MTT, LEV, TON and NES, IM-5 or a NU-85, NU-86, NU-88 zeolite.
U.S. Pat. No. 7,264,789 discloses a colloidal suspension of a LEV framework type crystalline molecular sieve and its use as seeds in the manufacture of a crystalline molecular sieve selected from the group consisting of the MFS, CHA, OFF, MOR, FER, MAZ, EUO and ERI/OFF, framework types.
U.S. Pat. No. 6,514,479, FR-A-2785201, WO-A1-2006/134249, FR-A-2785278, and the article entitled “The synthesis and characterization of zeolite EU-1”, in Proceedings of the International Zeolite Conference, 894-904 (1984), disclose the preparation of zeolites having the EUO framework type in the presence of seeds of an EUO framework type zeolite. The use of said seeds has the advantage to reduce the crystallization time of the EUO zeolite and to improve the flexibility in the reaction mixture composition.
According to the present invention it has now been found that, in the synthesis of EUO framework type crystalline molecular sieves, the use of colloidal seeds of previously synthesized EUO framework type material can be used to tailor the particle size and the particle size distribution of the as synthesized EUO framework type molecular sieves. In particular, the addition of increasing amounts of colloidal seeds of previously synthesized EUO framework type material allows the production of substantially single EUO crystals with tailored average size d50 values, as measured by laser scattering, decreasing to a minimum generally at around 1 μm or below.